Marina Krichevskaya

The Cost Evaluation of Advanced Oxidation Processes in Laboratory and Pilot-Scale Experiments

The present level of the development of water/wastewater treatment methods, including advanced oxidation processes, allows removal of pollutants of wide spectrum under no question. However, the overall process cost and, especially, associated energy consumption are of increased importance. The present review presents the energy cost calculations made for the pollutants removal reported in more than forty publications for over the last four decades. Phenol, glycols, methyl-tert-butyl ether (MTBE), aliphatic unsaturated compounds, humic acids and lignin were considered as water pollutants for economic evaluation of their removal. Two oxidation processes, ozonation and Fenton reaction, were chosen as water treatment methods.

Photocatalytic oxidation of aromatic aminocompounds in aqueous solutions and groundwater from abandoned military bases

Experimental research into the photooxidation of aqueous solutions and polluted groundwater containing aromatic aminocompounds was undertaken. For the experiments with synthetic solutions, titanium dioxide under near-UV irradiation was selected as a photocatalyst, and aniline, p-toluidine and 2,4-xylidine were selected as model compounds. The photooxidative treatment of synthetic solutions was found to be more effective in acidic and strongly alkaline media. Methylated aminocompounds (p-toluidine, 2,4-xylidine) yield slightly better to photooxidation than aniline. The results obtained from experiments using model compounds were compared with the results of photooxidative purification of polluted groundwater from an abandoned military base in Estonia. Being heavily polluted, the groundwater yields better to photooxidation when diluted with potable water at a 7:3 ratio. Anatase, immobilised onto the surface of buoyant hollow glass microspheres, was less effective than when suspended in slurry. However, the immobilised photocatalyst enables water to be treated without the expense of constant stirring. This also avoids complications concerned with catalyst separation following treatment. Degussa P25 was more effective than Aldrich anatase both in stirred slurry type reactors and when attached to hollow glass microspheres.

Aqueous photocatalytic oxidation of sulfamethizole

Aqueous photocatalytic oxidation (PCO) of a non‐biodegradable sulphonamide antibiotic sulfamethizole was studied. The impacts of photocatalyst dose, initial pH, and substrate concentration in the range from 1 to 100 mg L−1 were examined with a number of organic and inorganic by‐products determined, suggesting the initial break‐up of the SMZ molecule at the sulphonamide bond. The experiments were carried out under artificial near‐UV and visible light, and solar radiation using Degussa P25 and less efficient visible light‐sensitive C‐doped titanium dioxide as photocatalysts.

The influence of ferrous/ferric ions on the efficiency of photocatalytic oxidation of pollutants in groundwater.

The complex influence of ferrous/ferric ions on the efficiency of aqueous photocatalytic oxidation (PCO) of 2-ethoxyethanol (2-EE), methyl tert-butyl ether (MTBE) and humic substances (HS) was established. A drastic efficiency increase at lower concentration of ferrous/ferric ions was observed to change to a sharp decrease at higher concentrations for 2-EE and MTBE, whereas for HS only an inhibitive effect of Fe2+/3+ on the PCO efficiency was noticed. The authors proposed an explanation for the observed phenomena based on the different sensitivities of pollutants towards radical-oxidation reactions and the competitive adsorption of metallic ions and pollutants on the TiO2 surface.

Photocatalytic oxidation of fuel oxygenated additives in aqueous solutions

Experimental research of photocatalytical oxidation (PCO) of aqueous solutions of de-icing agents (ethylene glycol and ethylene glycol monoethyl ether) and methyl tert -butyl ether (MTBE) was un- dertaken. These chemicals are water-soluble components of jet and motor fuels accidentally disposed to the environment. Titanium dioxide (Degussa P25) under near-UV irradiation was selected as a photocata- lyst. A slightly acidic medium was preferable for the process efficiency for MTBE, whereas a neutral medium was beneficial for de-icing agents and jet fuel aqueous extracts. TiO2 suspension fractional composition was found to be dependent on pH and the presence of organic admixtures: the minimum size of TiO2 par- ticles at their maximum uniformity was established in an acidic medium, where the efficiency of PCO of de-icing agents was the poorest. On the other hand, neutral and slightly acidic media, beneficial for PCO effi- ciency, were favourable for particle agglomeration, which indicates a minimal role for photocatalyst particle size in PCO efficiency. PCO efficiency increased with increasing MTBE and icing inhibitor concentration. The biodegradability of aqueous solutions of oxygenated additives increased as PCO proceeded. The influence of mineral additives—sulphate, calcium, ferric and manganese ions—on the process efficiency was found to be complex. Special attention was paid to energy-saving PCO with a photocatalyst attached to buoyant glass micro-spheres and reduced intensity of stirring of the slurry.

Gas-phase photocatalytic oxidation of acrylonitrile

Photocatalytic oxidation (PCO) of acrylonitrile (AN) on titanium dioxide in the gaseous phase was studied. AN readily undergoes photocatalytic degradation in a gas-solid system by using TiO(2) Degussa P25. The AN PCO volatile products, visible in the infrared spectra, included nitrogen dioxide, nitrous oxide, carbon dioxide, water, hydrogen cyanide and carbon monoxide. Longer contact time resulted in deeper oxidation of AN with decreasing hydrogen cyanide and increasing nitrogen dioxide content. The effect of temperature increasing from 60 to 130 degrees C was observed to be slightly negative in terms of AN degradation rate. However, the effect of increased temperature was noticeable in terms of the character and yields of the PCO products: HCN peaks diminished with growing peaks of NO(2).

Photocatalytic decomposition of humic acids in anoxic aqueous solutions producing hydrogen, oxygen and light hydrocarbons

Photocatalytic water splitting for hydrogen and oxygen production requires sacrificial electron donors, for example, organic compounds. Titanium dioxide catalysts doped with platinum, cobalt, tungsten, copper and iron were experimentally tested for the production of hydrogen, oxygen and low molecular weight hydrocarbons from aqueous solutions of humic substances (HS). Platinum-doped catalyst showed the best results in hydrogen generation, also producing methane, ethene and ethane, whereas the best oxygen production was exhibited by P25, followed by copper – and cobalt-containing photocatalysts. Iron-containing photocatalyst produced carbon monoxide as a major product. HS undergoing anoxic photocatalytic degradation produce hydrogen with minor hydrocarbons, and/or oxygen. It appears that better hydrogen yield is achieved when direct HS splitting takes place, as opposed to HS acting as electron donors for water splitting.

Treatment of Phenolic and Aromatic Amino Compounds in Polluted Waters by Photocatalytical Oxidation

Abstract Improper handling of rocket fuel residues at abandoned military bases has resulted in heavy pollution of the soil and groundwater with aromatic amino compounds. A similar phenomenon is observed with ash dumps in which solid waste from oil shale thermal treatment is disposed: the ash dump leachate is heavily polluted with phenolic and other compounds, resistant to biological treatment. Experimental research of photocatalytical oxidation (PCO) of both classes of substances and polluted waters was undertaken. The influence of different parameters - pH, concentration of substances to be oxidised, character of substances formed during the PCO, presence of inorganic admixtures, effect of OH•-radical generators and scavengers - on the PCO of solutions of phenolic and aromatic amino compounds was determined. The role of OH•-radicals was found to be important in determining both the PCO rate and the character of the oxidation by-products. The PCO of organic pollutants was also investigated using a catalyst immobilised onto the surface of buoyant hollow glass micro-spheres. Attached titanium dioxide showed lower photocatalytical activity than its slurry, although it allows waters to be treated in simple shallow ponds without intensive stirring. The toxicity of aqueous solutions and polluted waters decreased as PCO proceeded and the biodegradability increased. The energy consumed by PCO of phenolic compounds in phenolic wastewater under solar radiation was estimated to be smaller than the energy consumed by oxidation with ozone.

Selective performance of sol-gel synthesised titanium dioxide photocatalysts in aqueous oxidation of various-type organic pollutants

Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants. The objective of the research consists in the synthesis and testing of photocatalytic activity of carbon-containing titanium dioxide photocatalysts calcinated at various temperatures. The optical and structural properties of the catalysts were also studied. The activity was tested in visible light in aqueous photocatalytic oxidation of three various-type pollutants, methyl-tert-butyl ether, p-toluidine and phenol, where the divergent character of the C-TiO2 catalysts was distinctively observed: methyl-tert-butyl ether and p-toluidine were oxidized with the efficiency close to or even surpassing that of UV-irradiated P25 (Evonik), whereas phenol was oxidized poorly. The observed photocatalytic activity, where quantum efficiency varied from 0.6 to 2.3 and from 0.1 to 1.2% for p-toluidine and phenol degradation respectively, may be explained by the different electrostatic properties of the catalysts’ surface and the tested substances, i.e. their interaction. This compromises the widespread usage of phenol as a reference substance for comparison of catalytic activities of catalysts.

Aqueous Photocatalytic Oxidation of Doxycycline

Abstract The experimental research into the aqueous photocatalytic oxidation of doxycycline, a tetracycline family antibiotic, was undertaken. The objective of the study was to ensure the feasibility of doxycycline photocatalytic degradation by UVA irradiated titania coatings on granulated media to be used in fluidised bed photocatalytic reactor and by slurries of P25, Evonik, as well as by visible light-sensitive sol-gel synthesized carbon-containing titania. The parameters influencing doxycycline oxidation, like catalyst concentration, initial doxycycline concentration and pH with P25 TiO2 were studied. The impact of calcination temperature on the catalytic properties of carboncontaining titania and catalytic activity of titania film on expanded clay as bed material towards doxycycline degradation were also studied. Based on the examination of doxycycline photocatalytic oxidation by-products, possible doxycycline degradation pathways were proposed.